RECORD BREAKING TEMPERATURES
SEEN AS POSSIBLE EVIDENCE OF FASTER RATE OF GLOBAL WARMING, NOAA
REPORTS

Researchers at the Commerce
Department's National Oceanic and Atmospheric Administration
have found evidence that indicates that the rate of global warming
is accelerating and that in the past 25 years it achieved the
rate previously predicted for the 21st century (2 degrees C per
century).

Writing in the March 1 issue of Geophysical Research Letters,
Thomas R. Karl, director of NOAA's
National Climatic Data Center
in Asheville, N.C., and his colleagues analyze recent temperature
data. They focus particularly on the years 1997 and 1998, during
which a string of 16 consecutive months saw record high global
mean average temperatures. This, Karl notes, was unprecedented
since instruments began systematically recording temperature
in the 19th century. During much of 1998, records set just the
previous year were broken.

Karl and colleagues conclude that there
is only a small chance that the string of record high temperatures
in 1997-1998 was simply an unusual event, rather than a change
point, the start of a new and faster ongoing trend. Since completing
the research, the data for 1999 has been compiled. The researchers
found that 1999 was the fifth warmest year on record, although
as a La Niña year it would normally be cooler. Outside
the band 20 degrees north latitude and 20 degrees south latitude,
1999 was the second warmest year of the 20th century, just behind
1998, an El Niño year.

The researchers at NCDC analyzed data from
land based and satellite instruments for their study. Using sophisticated
mathematical and probabilistic models in a series of experiments
they concluded that the rate of warming since 1976 is clearly
greater than the average rate over the late 19th and 20th centuries.
To account for the string of record-setting temperatures, the
average rate of global temperature increase since 1976 would
have to be three degrees Celsius (five degrees Fahrenheit) per
century.

In its Second Assessment Report
in 1995, the Intergovernmental Panel on Climate Change projected
the rate of warming for the 21st century to be between 1.0 and
3.5 degrees C. Karl and his colleagues have already observed
over the past 25 years a rate that is between 2 and 3 degrees
C per century. The IPCC study used a "business as usual"
scenario with regard to emissions of carbon dioxide and other
atmospheric constituents.

Karl and his colleagues aren't ready to
say for certain that the rate of global warming has suddenly
increased, because they know unusual events sometimes happen.
Given the steady increase in atmospheric greenhouse gases and
their decades-to-centuries atmospheric residence time, he urges
that studies be conducted to better understand how society can
minimize the risks of climate change and prepare for more, and
perhaps even more rapid changes to come.